The stability of molecular clouds

A local instability analysis of a self-gravitating partially ionized, warm, magnetized gas is used to study the stability of molecular clouds. It is found that wave propagation is possible for wavelengths longer than the critical frictional damping scale in clouds, as long as the magnetic and thermal energy densities exceed the gravitational energy density. The analysis is extended to the case in which a background spectrum of Alfven waves supports the cloud against global collapse. It is shown that the steepness of the wave spectrum is as important as the overall magnetization of the cloud in determining which modes become unstable. It is found that, for a wide range of wave spectra, the largest scales in a cloud can be supported against global collapse, while for a band of smaller wavelengths, gravitational collapse may occur. 30 refs